1. Field of the Invention
The present invention relates to a vacuum film-forming apparatus and a method of application thereof. More particularly, the present invention relates to a vacuum film-forming apparatus such as a sputtering apparatus, a vacuum deposition apparatus, or an ion plating apparatus, and also to a vacuum film-forming method, in which cooling water is supplied to a target assembly to cool the target.
2. Description of the Related Art
FIG. 1 is a sectional view showing an example of a conventional vacuum film-forming apparatus, such as an aluminum sputtering apparatus. In FIG. 1, the apparatus has a chamber 1, and a target assembly 2 including an aluminum target 2a (shown in FIG. 2) disposed on a wall of the chamber 1. An argon gas source 3 is connected to the chamber to allow argon gas to be introduced therein. The amount and the pressure of the argon gas supplied are adjusted by means of a mass flow controller (MFC) 4 and regulators 5 and 6, respectively. The interior of the chamber 1 is evacuated roughly by means of a hydraulic rotary pump 7 while an evacuating valve 7a and a pump leak valve 7b are also being used. The interior of the chamber 1 is then kept at a high level of vacuum by means of a cryopump 8 while a foreline valve 8a is also being used. A conveyance pallet 10 is disposed within the chamber 1, and a semiconductor wafer 9, on which aluminum is to be sputtered, is placed upon the pallet 10. A throttle valve 11 and a gate valve 12 are connected to the cryopump 8 to allow the rate of evacuation to be controlled.
FIG. 2 shows the target assembly 2 in detail. Pipes 2c and 2d, and a cooling water baffle 2g are provided behind the aluminum target 2a so that cooling water may flow on the periphery of the aluminum target 2a as well as toward a magnet 2b. This arrangement ensures that the temperature of various parts of the target assembly 2 is prevented from rising to and is maintained below an unnecessarily high level. An iron casing 2f is disposed on the upper surface of the magnet 2b, and a cathode body 2e is disposed surrounding the casing 2f and the magnet 2b. The cathode body 2e is connected to a DC power source 2n.
The target assembly 2 also includes a dark space shield 2h, and an anode 2i. The aluminum target 2a is fixed to the cathode body 2e by a clamp ring 2j and is fastened by screws 2k. The target assembly 2 is mounted on a chassis 2m via an insulating plate.
The conventional aluminum sputtering apparatus having the above-described construction operates in the following manner. A semiconductor wafer 9 is inserted into the chamber 1 through a load lock chamber (not shown). Subsequently, the evacuating valve 7a is opened and the hydraulic rotary pump 7 is operated in such a manner as to maintain the interior of the chamber 1 in a vacuum condition at a level on the order of 10.sup.-3 Torr. After the evacuating valve 7a has been closed, the gate valve 12 and the foreline valve 8a are opened, and the cryopump 8 is operated in such a manner as to maintain the interior of the chamber in a vacuum condition at a high level of about 10.sup.-7 to 10.sup.-8 Torr. Thereafter, argon gas is introduced into the chamber 1 from the argon gas bomb 3 while the rate of evacuation by the cryopump 8 is adjusted by means of the throttle valve 11, in such a manner that the interior of the chamber 1 is maintained in a vacuum condition at a low level of about 1 to 30 mTorr.
Thereafter, when electric power of 1 to 3 kW is applied between the cathode body 2e and the anode ring 2i by the DC power source 2n, Ar.sup.+ accelerated by the high voltage collides with the surface of the aluminum, target 2a. As a result, aluminum particles of atom size are discharged from the aluminum target 2a and are then sputtered onto the semiconductor wafer 9.
During this action, part of the energy generated by the collision of Ar.sup.+ is generated as heat. This heat, however, is by no means necessary for sputtering. Therefore, in order to protect the sputtering apparatus per se from the heat, cooling water is allowed to flow through the pipes 2c and 2d to the back of the target assembly 2, thereby water-cooling the assembly 2.
It is widely known that, in order to form good thin films, it is necessary to enhance the level of vacuum within the chamber 1. When it is desired to obtain a particularly good thin film, such as an aluminum thin film with only a very small number of hillocks, it is also necessary, in addition to eliminating any vacuum leakage, to thoroughly reduce residual impurity gases within the chamber 1, such as H.sub.2, H.sub.2 O, N.sub.2, and O.sub.2. For this purpose, therefore, such impurities must be effectively removed.
With the conventional aluminum sputtering apparatus having the above-described construction, however, the following problem is encountered. When the chamber 1 is opened, there is a risk that certain gases contained in the ambient atmosphere around the chamber 1, particularly moisture, may be introduced into the chamber 1 and condense on and adhere to the surface of various cooled component parts such as the pipes 2c and 2d. During sputtering, the moisture thus introduced may evaporate or decompose into a gas, which may cause degradation of the quality of an aluminum thin film being formed.